Please refer to FIG. 1A showing a conventional motor fan 1 which includes a stator 11, a rotor including a ring-type magnet 12 and a hub 14 having a plurality of blades circumferentially fixed on its surface, a printed circuit board 13, and a fan guard 15. The stator 11 is formed by disposing a silicon steel sheet 111 with a specific shape in the mold to be sheathed with an insulator 112 (that is, a potting process) for fabricating a bobbin on which a coil 113 is wound, as shown in FIGS. 1A ˜1C.
However, the surface of the silicon steel sheet 111 will be easily damaged due to high temperature during the potting process and the silicon steel sheet 111 will be easily covered with rust.